The present invention generally relates to a method for manufacturing an optical disk, an optical disk apparatus, and an optical disk. More specifically, the present invention is directed to an optical disk in which serial data such as positional information is recorded by, for example, wobbling grooves functioning as guide grooves for a laser beam, and an optical disk apparatus for accessing this optical disk. In particular, the present invention is related to a technique capable of specifying a laser beam irradiation position in high precision while grooves are wobbled in response to a phase-shifted signal.
Conventionally, in optical disks, since grooves functioning as guide grooves for guiding a laser beam are wobbled, positional information and time information of laser beam irradiation positions (will be referred to as xe2x80x9cwobble dataxe2x80x9d hereinafter) are detected (see U.S. Reissue Patent 34,719).
That is, in a manufacturing step for this sort of optical disk, while a mother disk is rotated at a preselected rotation speed, a laser beam is irradiated onto this mother disk, and this laser beam irradiation position is sequentially shifted toward an out peripheral side of the mother disk. As a result of this optical disk manufacturing step, the mother disk is sequentially exposed by the laser beam to form a track in a helical form from an inner peripheral side of this mother disk to the outer peripheral side thereof.
In the optical disk manufacturing step, a stamper is formed from this mother disk through a developing step and an electrocasting (electroforming) process step, and then an optical disk is formed by this stamper. As a consequence, in this optical disk, the groove is formed in the helical shape from the inner peripheral side of this optical disk to the outer peripheral side thereof in correspondence with the laser beam irradiation position on the mother disk.
When the mother disk is exposed in the above-described manner, as indicated in FIG. 1, in the manufacturing step for the optical disk, a reference signal which is synchronized with a predetermined carrier signal is frequency-divided to thereby produce a clock (see FIG. 1B). Furthermore, both a first reference signal which is synchronized with this clock CK, and a second reference signal constituted by a xc2xd-frequency-divided signal of the clock CK are arranged in response to a logic level of wobble data D1 (see FIG. 1A), respectively. As a result, the wobble data D1 is biphase-mark-modulated (see FIG. 1A, FIG. 1B, and FIG. 1C). In addition, a sync pattern is inserted into a serial data stream produced by biphase-mark-modulating such wobble data D1 to thereby produce a channel signal xe2x80x9cchxe2x80x9d. Thereafter, the carrier signal which is used to generate the clock CK is frequency-modulated by this channel signal xe2x80x9cchxe2x80x9d, so that a frequency-modulated signal (will be referred to as a xe2x80x9cwobble signalxe2x80x9d hereinafter) WB is produced. In the manufacturing step of the optical disk, an irradiation position of a laser beam is shifted, or deviated along the radial direction of the mother disk in order to follow a signal level of this wobble signal WB.
As a result, as shown in FIG. 2, in this sort of optical disk, a groove is formed in such a manner that this groove is wobbled in response to a sync pattern and ID data. A spindle motor is controlled in such a manner that a center frequency of this wobble becomes a predetermined frequency, so that this optical disk is rotated at a preselected rotation speed. While using this wobble as a reference, the ID data is detected in order that the recording/reproducing position can be confirmed. Also, various sorts of processing reference clocks can be produced on the basis of this wobble (see FIG. 2A to FIG. 2C).
In accordance with this wobbled groove, the information recording plane can be effectively utilized, as compared with such an optical disk case that address data and the like are recorded by using a prepit. Moreover, the timing control can be easily performed during the recording operation. In addition, this preformatted groove type optical disk owns such a feature that compatibility can be readily established with a reproduction-only optical disk in which data is recorded by using a pit.
Moreover, in the conventional ID data recording method by the groove, the positional information can be detected in sufficient precision along the radial direction of the optical disk, whereas there is such a problem that the positional information could not detected in high precision along the rotation angle direction of the optical disk. Accordingly, if this problem can be solved, then the desirable data may be recorded in further high density in the conventional recording method.
The present invention has been made to solve the above-described problem, and therefore has an object to provide a method for manufacturing an optical disk, an optical disk, and also an optical disk apparatus, capable of specifying a laser beam irradiation position while desirable data is recorded by using a wobbled groove.
In an optical disk and an optical disk manufacturing method, according to the present invention, a phase-modulated signal is produced, and then a groove of the optical disk is wobbled in response to a signal level of this phase-modulated signal.
In this phase-modulated signal, time periods of the wobbled grooves can be kept constant. Also, in a wobble signal produced by detecting this wobbled groove, a single frequency is maintained. As a result, a clock having high precision can be generated based upon the frequency information of this wobble signal. Thus, angular information can be detected in high precision as to a laser beam irradiation position by using this clock having such high precision.